Structural analysis of membrane-bound O-acyltransferases Abstract: Membrane-bound O-acyltransferases (MBOATs) form a superfamily of membrane- embedded enzymes, which have 8-12 predicted transmembrane helices and catalyze the transfer of acyl groups to metabolites or secreted proteins. MBOATS are conserved from bacteria to human and play important roles in many biological processes. In human, MBOAT proteins catalyze acylation of some critical metabolites including diacylglycerol and cholesterol, and are responsible for lipid modification and maturation of secreted signaling proteins/peptides, including Wnt, hedgehog and ghrelin. In this project, we will focus on crystallographic and biochemical analysis of two MBOAT proteins: DltB that catalyzes D-alanylation of cell wall teichoic acid in Gram-positive bacteria, and porcupine (PORCN) that is responsible for palmitoylation of Wnt proteins. With our first MBOAT target, DltB, we have already obtained multiple crystal forms and solved the DltB crystal structure. We will complete and refine our DltB crystal structures, and aim to understand how DltB recognizes its cytoplasmic D-alanyl group donor protein DltC and extracellular acceptor lipoteichoic acid (LTA). This study will provide a paradigm for understanding MBOAT superfamily 3D structures and how MBOAT family members catalyze O-acyl transfer. It may also provide new insights into novel antibiotics development. With our second target, PORCN, we will reveal its 3D structure using a combination of X-ray crystallography, computational modeling and biochemical analysis. Wnt proteins play crucial roles in many important biological processes. PORCN activity is essential for Wnt secretion and Wnt signaling activity, and PORCN inhibitors are being evaluated in multiple anticancer clinical trials. Our work will lead to much-anticipated understanding of the molecular basis of PORCN-mediated Wnt palmitoylation, and provide structural basis for the development of highly potent PORCN inhibitors.